In conventional medical diagnostic imaging the object is to obtain an image of a patient's internal anatomy with as little X-radiation exposure as possible. The fastest imaging speeds are realized by mounting a dual-coated radiographic element between a pair of fluorescent intensifying screens for imagewise exposure. About 5% or less of the exposing X-radiation passing through the patient is adsorbed directly by the latent image forming silver halide emulsion layers within the duplitized radiographic element. Most of the X-radiation that participates in image formation is absorbed by phosphor particles within the fluorescent screens. This stimulates light emission that is more readily absorbed by the silver halide emulsion layers of the radiographic element.
Examples of radiographic element constructions for medical diagnostic purposes are provided by U.S. Pat. No. 4,425,425 (Abbott et al.) U.S. Pat. No. 4,425,426 (Abbott et al.), U.S. Pat. No. 4,414,310 (Dickerson), U.S. Pat. No. 4,803,150 (Dickerson et al.), U.S. Pat. No. 4,900,652 (Dickerson et al.), U.S. Pat. No. 5,252,442 (Tsaur et al.), and U.S. Pat. No. 5,576,156 (Dickerson), and Research Disclosure, Vol. 184, August 1979, Item 18431.
Problem to be Solved
Image quality and radiation dosage are two important features of film-screen radiographic combinations (or imaging assemblies). High image quality (that is high resolution or sharpness) is of course desired, but there is also the desire to minimize exposure of patients to radiation. Thus, “high speed” imaging assemblies are needed. However, in known imaging assemblies, the two features generally go in opposite directions. Thus, imaging assemblies that can be used with low radiation dosages (that is, “high speed” assemblies) generally provide images with poorer quality (poorer resolution). Lower speed imaging assemblies generally require higher radiation dosages.
Conventional radiographic film-screen combinations, known as imaging assemblies (or systems), useful for general radiography, may have a total system speed of up to 400 but lack sufficient crossover control. The use of higher speed films in such assemblies may not be useful because of a need to control fog or unwanted density in the non-imaged areas of the film.
There is a need for high speed imaging assemblies that are useful especially for general-purpose radiography that require minimum radiation dosages with minimal sacrifice in image quality (for example, resolution or sharpness).